And the smartphone said, “Let there be light.” The new Light Bulb Finder (free) recommends specific energy-saving bulbs based on user-?provided information;users can then buy the bulbs with just a few taps.

In addition to being green, switching to energy-efficient lighting can save a household more than $120 a year, according to calculations based on data from the U.S. Energy Information Administration and the U.S. Department of Energy.